Carbohydrate-based peritoneal dialysis fluid comprising glutamine residue

ABSTRACT

The present invention relates to a carbohydrate-based peritoneal dialysis fluid, containing a compound selected from the group consisting of glutamine, preferably L-glutamine; a dipeptide capable of releasing glutamine, L-glutamine in free form, preferably selected from the group consisting of glutaminyl-glycine, glycinyl-glutamine, glutaminyl-alanine, alanyl-glutamine; an oligopeptide consisting of two to seven glutamine, preferably L-glutamine residues; and mixtures thereof. The peritoneal dialysis fluids of the present invention are useful for inhibition of technical failure in a person undergoing peritoneal dialysis treatment.

This application is a Continuation of U.S. patent application Ser. No.12/529,537 filed on Sep. 1, 2009, which is the National Phase of PCTInternational Application No. PCT/AT2008/000072 filed on Mar. 3, 2008,which claims priority under 35 U.S.C. 119(a) to Austrian PatentApplication No. A 340/2007 filed on Mar. 2, 2007, all of which arehereby expressly incorporated by reference into the present application.

The present invention relates to a peritoneal dialysis fluid (in thefollowing also referred to as “PDF”).

Peritoneal dialysis fluids remove solutes and water from the uremicpatient. Several clinical and experimental observations have shown thatPDF is cytotoxic, associated with a risk of technical failure of up to30% with long term peritoneal dialysis (PD) treatment (6). Therefore,prolonged PD treatment frequently results in severe chronic damage tothe integrity of the peritoneal membrane. Bio-incompatibility of PDF andperitoneal inflammation are regarded as the major culprits. PDF exposureimpairs peritoneal cell metabolism, reduces proliferation and increasescell death, as well as disrupts cytoskeletal organization and cellsignaling, including the regulation of differentiation and inflammation.This results in aberrant healing processes, epithelial-mesenchymaltransdifferentiation, neoangiogenesis, fibrosis and chronic scarring ofthe peritoneal membrane (7). Analysis of sequential peritoneal biopsyspecimens from patients undergoing PD revealed deleterious structuralalterations. In severe cases, mesothelial cells have detached, theperitoneum is denuded and covered with a thick amorphous layer ofconnective tissue. These morphological changes result in severedisruption of the barrier function of the peritoneum as a semi-permeabledialysis membrane. Up to a third of adult patients on PD will sufferfrom technical failure during the course of the treatment because ofperitoneal membrane failure (6).

Current research therefore aims to increase biocompatibility of PDF andthereby reduce mesothelial cell damage during PD. New and improvedformulations have indeed shown to be less toxic in several in-vitro andin-vivo, experimental and clinical studies (7,10). Addition of theantioxidant/scavenger Carnosine (a β-alanyl-L-histidine dipeptide), orGlutathion (gamma-glutamyl-L-cysteinyl-glycine) and related compounds(such as the cysteine prodrug L-2-oxothiazolidine-4-carboxylate) wereshown to have a positive influence on PDF biocompatibility and topassively reduce the deleterious impact of glucose degradation productsin PD (20-22).

However, the main working principle of PDF is removal of solutes andwater from the uremic patient due to its hypertonicity. PDF willtherefore likely never represent a physiologically inert or completelybiocompatible fluid and repeated filling and drainage to and from theabdominal cavity will always retain some cytotoxicity.

The above-mentioned disadvantages especially apply to carbohydrate-basedPDF. Under “carbohydrate-based” PDF the skilled artisan understands aperitoneal dialysis fluid based on glucose or glucose-oligomers andglucose-polymers as the osmotic agent. PDF's based on glucose arepreferably used in the present invention and may typically contain from10 to 45 g/1 glucose (cf. EP 1 166 787). Further examples ofcarbohydrate-based PDF's are disclosed in WO 82/03773 A1, U.S. Pat. No.4,976,683 A, WO 01/02004 A1, US 2003/0232093 A1, EP 1 369,432 A2, KR2001/008659, WO 94/14468 A1, WO 99/01144 A1, U.S. Pat. No. 6,077,836 A,WO 95/19778 A1, US 2005/0074485 A1, EP 0 207 676 A2 and WO 93/14796.

Recently, it was demonstrated that cytotoxicity of, especially,glucose-based PDF not only results in cellular injury, but alsoactivates an endogenous machinery found in every cell, the heat-shockproteins (HSP) in mesothelial cells in in-vitro, ex-vivo and in-vivomodels of PD (1-4,16). Whereas earlier studies focused on HSPupregulation as a marker of PDF biocompatibility, more recent data madeevident that HSP protect mesothelial cells during experimental PD(3,5,9).

Overexpression of HSP resulted in survival of an usually lethal PDFexposure in the in-vitro model of PD and prevented mesothelial cellsfrom detachment from their peritoneal lining in the in-vivo model of PD(5,9).

However, none of the used protocols to induce overexpression of HSP—suchas hyperthermia or transient transfection—are attractive approaches inthe clinical setting of PD.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a carbohydrate-basedperitoneal dialysis fluid which has less cytotoxicity than previouslyknown products. Especially, it is an object of the present invention toprovide a carbohydrate-based peritoneal dialysis fluid which inhibitstechnical failure in a patient undergoing a PD-treatment by activelyoptimizing cellular responses to pathophysiological stress upon PDFexposure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: The viability effects of L-glutamine exposure on cultured humanmesothelial cells.

FIG. 2: HSP-72 expression in human mesothelial cells after exposure toincreasing doses of glutamine.

FIG. 3: LDH release by cultured human mesothelial cells afterPDF-exposure.

FIG. 4: HSP-72 expression after exposure to PDF with or without addedglutamine.

FIG. 5: Effect of pharmacologic manipulation of HSP-72 expression onmesothelial cell detachment.

FIG. 6: Effect of pharmacologic manipulation of HSP-72 expression onperitoneal protein loss in the rat model of peritoneal dialysis.

DETAILED DESCRIPTION

The term “technical failure” is well-known to the skilled artisan andmeans the need to terminate peritoneal dialysis, and to switch toalternate renal replacement therapies such as hemodialysis (6).Especially inhibiting technical failure includes steps to preventperitoneal membrane failure and to attenuate barrier dysfunction and toprevent mesothelial cell detachment.

This object is solved by a carbohydrate-based peritoneal dialysis fluidcontaining a compound selected from the group consisting of

-   -   glutamine, preferably L-glutamine,    -   a dipeptide capable of releasing glutamine, preferably        L-glutamine, in free form, preferably selected from the group        consisting of glutaminyl-glycine, glycinyl-glutamine,        glutaminyl-alanine and alanyl-glutamine    -   an oligopeptide consisting of two to seven glutamine, preferably        L-glutamine residues and    -   mixtures thereof.

Furthermore, this object is solved by a compound selected from the groupconsisting of

-   -   glutamine, preferably L-glutamine,    -   a dipeptide capable of releasing glutamine, L-glutamine in free        form, preferably selected from the group consisting of        glutaminyl-glycine, glycinyl-glutamine, glutaminyl-alanine and        alanyl-glutamine    -   an oligopeptide consisting of two to seven glutamine, preferably        L-glutamine residues and    -   mixtures thereof        for the specific use of inhibiting technical failure in a        peritoneal dialysis treatment with a carbohydrate-based        peritoneal dialysis fluid.

The object of the present invention is also solved by acarbohydrate-based peritoneal dialysis fluid comprising a compoundselected from the group consisting of

-   -   glutamine, preferably L-glutamine,    -   a dipeptide capable of releasing glutamine, preferably        L-glutamine, in free form, preferably selected from the group        consisting of glutaminyl-glycine, glycinyl-glutamine,        glutaminyl-alanine and alanyl-glutamine    -   an oligopeptide consisting of two to seven glutamine, preferably        L-glutamine residues and    -   mixtures thereof        for the specific use of inhibiting technical failure.

It has surprisingly been found that glutamine induces HSP-expression inmesothelial cells. Moreover, it has been found that a carbohydrate-baseddialysis fluid containing glutamine, or a dipeptide capable of releasingglutamine in free form, such as glutaminyl-alanine and alanyl-glutamine,has lower cytotoxicity than previously known products. The use ofglutamine containing dipeptides such as glutaminyl-glycine andglycinyl-glutamine as precursors of glutamine is also advantageous.

Glutamine is non-toxic and has been previously reported to mediatecytoprotection by increasing HSP expression (14,18). In-vitro,pharmacologic doses of glutamine resulted in enhanced DNA binding ofHSF-1 to its promoter, similar as described for indomethacine and otherNSAIDs (11,12). Alternately, glutamine supplementation has shown toresult in stabilization of HSP-72 mRNA under stressful conditions,thereby increasing HSP expression (8). However, the use of glutamine toenhance HSP-expression in mesothelial cells when exposed to PDF has notyet been proposed.

According to the present invention, glutamine may be used in itsmonomeric form and/or in the form of a dipeptide capable of releasingglutamine in free form. It is known that the administration of aminoacids to mammals is better tolerated if they are administered in theform of a di- or tripeptide. Especially, glutamine is poorly soluble inaqueous solutions and is a relatively unstable amino acid and istherefore preferably used in the clinical setting as a dipeptideconsisting of glutamine and another amino acid, preferably alanine andglycine (23). Dipeptides containing L-glutamine as a component are,e.g., disclosed in U.S. Pat. No. 5,189,016.

Said dipeptide is preferably selected from the group consisting ofalanyl-glutamine, glutaminyl-alanine, glutaminyl-glycine andglycinyl-glutamine.

In a preferred embodiment, the PDF according to the present inventioncontains said compound in an amount sufficient to enhance expression ofHeat-Shock-Protein (HSP) in mesothelial cells.

The concentration of said compound, especially L-glutamine, in the fluidmay range from 0.3 mM to 300 mM, preferably from 2 mM to 25 mM.

The peritoneal dialysis fluid according the present invention may beproduced by a process which comprises the step of admixing the compound(i.e. glutamine in monomeric form or as a component of an oligopeptideas defined above) to a carbohydrate-based peritoneal dialysis fluid. Thecarbohydrate-based peritoneal dialysis fluid used for making the PDFaccording to the invention may be a standard product as currentlycommercially available.

Preferably, the compound is admixed to the carbohydrate-based peritonealdialysis fluid in an amount sufficient to enhance expression ofHeat-Shock-Protein (HSP) in mesothelial cells.

The present invention, furthermore, relates to the use of compoundselected from the group consisting of

-   -   glutamine, preferably L-glutamine,    -   a dipeptide capable of releasing glutamine, preferably        L-glutamine, in free form, preferably selected from the group        consisting of glutaminyl-glycine, glycinyl-glutamine,        glutaminyl-alanine and alanyl-glutamine    -   an oligopeptide consisting of two to seven glutamine, preferably        L-glutamine residues and    -   mixtures thereof        for the preparation of a carbohydrate-based peritoneal dialysis        fluid for inhibiting technical failure.

For all embodiments, the PDF employed is preferably based on glucose.

The present invention is explained in more detail in the following onthe basis of examples and figures exemplifying preferred embodiments ofthe invention.

In this regard, FIGS. 1 and 2 show the effects of L-glutamine exposureon cultured human mesothelial cells. Viability was assessed by LDHrelease (FIG. 1) and HSP-72 expression (FIG. 2) after exposure toincreasing doses of glutamine (GLN) under control conditions. Additionof L-glutamine up to 20 mM resulted in unchanged viability. HSP-72expression was enhanced at 8 and 10 mM glutamine concentration. Data arerepresentative for 3 independent experiments.

FIGS. 3 and 4 show the effect of L-glutamine during PDF-exposure oncultured human mesothelial cells. Viability was assessed by LDH release(FIG. 3) and HSP-72 expression FIG. 4) after exposure to PDF with orwithout added glutamine (GLN) for 120 min. Data are shown as box (25thand 75th), whiskers (10th and 90th percentile) and median plot. Additionof L-glutamine resulted in significantly preserved viability andincreased HSP-72 expression. Data are obtained from 6 experiments, thedetailed statistics are given in the results section.

FIGS. 5 and 6 show the effects of pharmacologic manipulation of HSP-72expression on mesothelial cell detachment and peritoneal protein loss inthe rat model of peritoneal dialysis. HSP-72 expression in ratmesothelial cells harvested by trypsin peritoneal washout after a 4-hourdwell with either standard PDF (PDF) or PDF with added L-glutamine(GLN-PDF) was investigated. Addition of L-glutamine resulted in enhancedHSP-72 expression. Mesothelial cell detachment (FIG. 5) and peritonealprotein loss (FIG. 6) are shown as box (25th and 75th), whiskers (10thand 90th percentile) and median plots. L-glutamine addition to PDF wasassociated with significantly lower mesothelial cellular (MC) counts anddecreased protein loss into the dialysate effluate. Data are obtained in6 rats in each group in 3 independent experiments.

Material and Methods

In-Vitro Model of PD (Adapted from Reference No. 5)

Immortalized human mesothelial cells (Met5A, ATCC CRL-9444) werecultured in M199/MCDB 105 medium (1:1) supplemented with 100 units/mlpenicillin, 100 μg/ml streptomycin and 10% FCS. Cultures were kept in 75cm² tissue culture flasks (Falcon, Becton Dickinson, Oxnard, Calif.) at37° C. in 5% CO₂ and passaged by regular trypsinization. Medium waschanged every two to three days. Confluence was reached on average after6 to 7 days.

Confluent cultures were then exposed for 120 minutes to standardglucose-monomer and acidic lactate-based PDF (Fresenius 2, Bad Homburg,Germany), containing 1.5% anhydrous dextrose at pH 5.5, with or withoutaddition of cytoprotective compound (glutamine at 4 to 20 mM) andallowed to recover in regular growth medium for 16 hours. Controlcultures were kept in regular culture media at 37° C. and underwent“sham media changes”, i.e.: exposure to PDF was paralleled by exposureto control medium.

Viability of cells was assessed by lactate dehydrogenase (LDH) analyses.Fifty μl aliquots of supernatants were removed after the describedexperimental setup and kept on 4° C. until analyzed within 48 hours.Measurements were performed in duplicates with Sigma TOX-7 LDH Kitaccording to the manufacturer instructions. LDH efflux was calculated aspercentage of LDH values measured in each negative control experiment.Induction of HSP was assessed in parallel cultures as described below.

In-Vivo Acute Rat Model of PD (Adapted from Reference No. 9):

The studies were carried out on adult male inbred Sprague Dawley rats(average weight 310 g). After introduction of anaesthesia (ketamine 100mg/kg and 5 mg/kg xylazine, intramusculary) the animals were placed on aheated small animal operating table. A sterile catheter was insertedinto the peritoneal cavity through a small abdominal midline incisionand 35 ml of test fluid (PDF with or without addition of L-glutamine at4-10 mM) were slowly infused in 45-60 secs. The animal was gently moved,a small volume of peritoneal fluid aspirated, the catheter withdrawn andthe abdomen sutured. Animals awoke within 20 minutes after the procedureand had free access to food and tap water. At 4 hours after theintraperitoneal injection animals were again anaesthetized, anothersmall volume of peritoneal fluid was aspirated and animals weresacrificed by cardial puncture and exsanguinations. Thereafter, theabdomen was opened by a midline incision and the completeintraperitoneal fluid gently collected. The volumes of the collectedfluids were recorded, and total cell count and differential counts atthe two time pints (0 and 4 hours) were assessed by hand count aftergiemsa staining and by machine count by a coulter counter. Total numberof detached mesothelial cells was then computed for each rat. Inselected animals, mesothelial cells lining the peritoneal cavity wereharvested following the 4 hour dwell by peritoneal washout with 20 mLphosphate-buffered saline (PBS) containing 0.1% trypsin and 0.1% EDTAfor 20 minutes.

For testing the barrier function of the peritoneal membrane, creatinine,glucose and total protein were measured in dialysate (D) samples andcreatinine in plasma (P) at the end of the protocol. D/P ratios forcreatinine and D/D0 ratios for glucose were computed. Peritoneal loss ofprotein was calculated as final dialysate concentration×final volume.All animals received humane care in compliance with the principles oflaboratory animal care as prepared by the National Academy of Sciencesand published by the National Institutes of Health.

HSP-72 Detection, and Statistics:

Western blotting: Protein content of mesothelial cell harvests wasdetermined by Bradford assay (BioRad) and equal amounts of proteinsamples (5 μg/lane) were separated by standard SDS-PAGE using aPharmacia Multiphore II unit. Size-fractionated proteins weretransferred to PVDF membranes by semi-dry transfer in a PharmaciaMultiphore II Novablot unit. Membranes were blocked in 5% dry milk inTBS-Tween (10 mM Tris, 150 mM NaCl, 0.05% Tween 20, pH 8.0). Membraneswere incubated with the HSP-72 antibody (SPA 810, Stressgen, B.C.,Canada). Detection was accomplished by incubation with secondary,peroxidase-coupled antibodies (Sigma, USA) and enhancedchemiluminescence (ECL) using ECL Western blotting analysis system andprotocols (Renaissance, NEN-Life Science Products, Boston, Mass., USA).Densitometry was performed with image analysis software (MolecularAnalyst software, Bio-Rad, USA). Differential expression of HSP-72 wasderived from the ratio of specific signals in the linear range of theprotein/signal intensity relationship, normalized to an internalstandard, and compared between parallel experiments.

Statistical analysis: Effects of treatments (+/−PDF exposure,+/−addition of cytoprotective additive (L-glutamine) were compared bymultifactorial ANOVA in the in-vitro experiments. In the in-vivoexperiments, effects of PDF exposure with versus without Glutamineaddition were compared using the Mann-Whitney U test (Statview IV,Abacus, USA). Differences were considered to be significant given ap<0.05. The data are expressed as means+/−S.D.

Results

Cytoprotective Effect of L-Glutamine

The in-vitro experiments demonstrate HSP-mediated cytoprotection inmesothelial cells following addition of L-glutamine to the PDF.

FIGS. 1 and 2 demonstrate the effects of exposure to increasing doses ofL-glutamine on cultured human mesothelial cells under controlconditions. Addition of L-glutamine up to 20 mM resulted in unchangedviability, levels of 8 and 10 mM were associated with increased HSP-72expression.

Effects of L-glutamine during standard PDF exposure on cultured humanmesothelial cells are shown in FIGS. 3 and 4. Addition of L-glutamine tothe PDF resulted in preserved viability and increased HSP-72 expression.LDH release increased from 100+/−3% under control conditions to226+/−29% during exposure to PDF without cytoprotective agent versus91+/−7 to 190+/−19% during exposure to PDF with added L-glutamine (FIG.3). Multifactorial ANOVA demonstrated that effects of PDF exposure andeffects of L-glutamine addition were both significant (p=0.0001 andp=0.001). These effects were interdependent, i.e. the (cytoprotective)effects of L-glutamine were significantly higher during (cytotoxic) PDFexposure (p=0.037).

HSP-72 expression increased from 100+/−43% under control conditions to423+/−661% during exposure to PDF without cytoprotective agent versus234+/−221 to 1895+/−1928 during exposure to PDF with added L-glutamine(FIG. 4). Again, multifactorial ANOVA demonstrated that effects of PDFexposure and effects of L-glutamine addition were both significant(p=0.003 and p=0.023). In addition, these effects were interdependent,i.e. the (HSP co-inducing) effects of L-glutamine were significantlyhigher during PDF exposure (p=0.011).

To confirm the biological role of pharmaceutical HSP-mediatedcytoprotection in PD, the effects of enhancing HSP-72 expression byL-glutamine supplemented PDF on mesothelial cell detachment from theirperitoneal monolayer in the rat model of PD were assessed. As shown inFIGS. 5 and 6, use of this cytoprotective PDF resulted in overexpressionof HSP-72, and significantly reduced mesothelial cell detachmentfollowing in-vivo PDF exposure during a 4 hr dwell (93+/−39 cells vs38+/−38 cells, p=0.044; FIG. 5). L-glutamine addition to PDF was alsoassociated with decreased protein loss into the dialysate effluate(75+/−7 mg vs 65+/−4 mg, p=0.045; FIG. 6). There were no effects ofL-glutamine supplementation on net ultrafiltration (6.8+/−1.1 ml vs5.4+/−2.7 ml), D/P creatinine (0.414+/−0.08 vs 0.375+/−0.11) or D/Doglucose (0.473+/−0.02 vs 0.469+/−0.04).

According to the above examples, in an in-vitro model of PD, addition ofL-glutamine resulted in marked HSP overexpression and improvedmesothelial cell survival during PDF exposure.

These in-vitro findings therefore link HSP expression and cellularoutcome in mesothelial cells, and clearly support the concept that apharmacologic additive can induce HSP-mediated cytoprotection againstPDF exposure.

In the final part of this study, HSP expression in the rat model of PDwas manipulated by adding the HSP co-inducer L-glutamine to PDF. Asexpected from the in-vitro results, L-glutamine supplementation enhancedHSP expression in mesothelial cells during in-vivo exposure. Consistentwith the concept of HSP-mediated cytoprotection, L-glutamine addition toPDF also resulted in a lower number of detached mesothelial cells. Ingood agreement with stabilization of the peritoneal mesothelialmonolayer, evidence for an attenuated barrier dysfunction was found, asdemonstrated by a lower protein content in the PD effluent of thetreated rats. The in-vivo experiments thus extend the previous findingsfollowing heat-pretreatment to a more feasible pharmacologicalintervention model (9).

Links between increased HSP expression and improved outcome are alsodescribed in animal survival models of sepsis and hyperthermia followingglutamine supplementation (17). In a small human randomized controlledtrial in ICU patients, there was also a significant correlation betweenincreases in serum HSP-70 and decrease in length of ICU stay followingglutamine supplementation during parenteral nutrition (19). Finally,patients with critical disease have been shown to frequently suffer fromglutamine depletion, supporting the potential for glutaminesupplementation in that population (13).

Cytoprotective Effect of a Dipeptide Capable of Releasing L-glutamine inFree Form.

The acute recovery experimental setting as described for glutamine as aproof of principle for the cytoprotective PDF, is best representativefor the early toxic effects of PDF, mainly due to low pH and lactate asmajor culprits. Alternate models such as a longterm exposure model tounused PDF diluted 1:1 with normal culture medium are better acceptedtools to assess effects of cellular processes that occur in theperitoneum upon more extended exposure to PDF, as occurs in clinical PD.

Therefore, L-alanyl-L-glutamine is tested for its potential to confercytoprotective effects by exposing confluent cultures for 24 hours toconventional acidic lactate-based PDF, containing 1.5% anhydrousdextrose, diluted 1:1 with M199 medium containing 10% FCS without orwith addition of L-alanyl-L-glutamine at a concentration of 0.5 and 10.0g/L (“low and high dose”). Additional control cultures are kept in pureregular culture media at 37° C. for the same time. At the end of thestudy, cell viability and protein expression are assessed in parallelcultures to identify the cytoprotective PDF.

The in-vitro experiments demonstrate HSP-mediated cytoprotection inmesothelial cells following exposure to PDF with addition ofL-alanyl-L-glutamine similar to what had been demonstrated forglutamine. The cytoprotective PDF containing L-alanyl-L-glutamineresults in preserved viability assessed by LDH release and increasedHSP-72 expression when compared to standard PDF exposure.

Taken together, the concordant effects of the novel PDFs according tothe present invention on HSP expression and cellular outcome clearlysupport the concept of HSP mediated cytoprotection in PD. Morespecifically, a high potential for L-glutamine as an additive to PDF tooptimize mesothelial cellular responses to pathophysiological stressupon in-vitro and in-vivo PDF exposure was delineated. Such HSP mediatedcytoprotection upon glutamine addition to PDF will likely havebiological relevance, as it was associated with decreased mesothelialcell detachment and lower peritoneal protein loss following acute PDFexposure. Given the deranged glutamine metabolism in patients withchronic renal failure, glutamine, and dipeptides capable of releasingglutamine in free form represent an extremely attractive candidate as“cytoprotective additive” to PDF (15).

REFERENCES

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The invention claimed is:
 1. A glucose-based peritoneal dialysis fluidcomprising: a peritoneal dialysis fluid comprising glucose; and adipeptide that is glutaminyl-glycine, glycinyl-glutamine,glutaminyl-alanine or alanyl-glutamine, or a mixture of two or more ofsaid dipeptides, wherein the concentration of said dipeptide in thedialysis fluid is 2 mM to 25 mM, wherein the glucose concentration inthe dialysis fluid is 10 g/l to 45 g/l, and wherein the glucose-basedperitoneal dialysis fluid does not include glutamine in its monomericform and wherein the glucose-based peritoneal dialysis peritonealdialysis fluid only contains amino acids in dipeptide form.
 2. Theperitoneal dialysis fluid according to claim 1, wherein said dipeptideis at least one member selected from the group consisting ofalanyl-glutamine and glutaminyl-alanine.
 3. The peritoneal dialysisfluid according to claim 1, wherein said dialysis fluid comprisesalanyl-glutamine.
 4. The peritoneal dialysis fluid according to claim 1,wherein the peritoneal dialysis fluid is suitable for use in peritonealdialysis in a patient.
 5. The peritoneal dialysis fluid according toclaim 1, wherein the glutamine is L-glutamine.
 6. A glucose-basedperitoneal dialysis fluid consisting essentially of: a peritonealdialysis fluid comprising glucose; and a dipeptide that isglutaminyl-glycine, glycinyl-glutamine, glutamine-alanine oralanyl-glutamine, or a mixture of two or more of said dipeptides,wherein the concentration of said dipeptide in the dialysis fluid is 2mM to 25 mM, wherein the glucose concentration in the dialysis fluid is10 g/l to 45 g/l and wherein the glucose-based peritoneal dialysis fluidonly contains amino acids in dipeptide form.
 7. The peritoneal dialysisfluid according to claim 6, wherein said dipeptide is at least onemember selected from the group consisting of alanyl-glutamine andglutaminyl-alanine.
 8. The peritoneal dialysis fluid according to claim6, wherein said dialysis fluid comprises alanyl-glutamine.
 9. Theperitoneal dialysis fluid according to claim 6, wherein the peritonealdialysis fluid is suitable for use in peritoneal dialysis in a patient.10. The peritoneal dialysis fluid according to claim 6, wherein theglutamine is L-glutamine.
 11. A method for preparing the glucose-basedperitoneal dialysis fluid of claim 1 comprising admixing a dipeptidethat is glutaminyl-glycine, glycinyl-glutamine, glutaminyl-alanine oralanyl-glutamine, or a mixture of two or more of said dipeptides, with acarbohydrate-based peritoneal dialysis fluid to provide a finalconcentration of said dipeptide of from 2 mM to 25 mM.